Enhanced late Holocene flaming fires in the NE Tibetan Plateau: coupled impacts of climate and human activities

Investigating the intricate connection among the combustion types (smoldering v.s. flaming), human activity and climatic patterns is is crucial for understanding the mechanisms of paleo-fire occurrences. This interaction requires further clarification, especcially in the NE Tibetan Plateau, due to the dramatic climatic and human activity shifts during the mid-late Holocene. Here, we examined the black carbon (BC, comprising char and soot) content within sediments from Caodalian (CDL) lake spanning the past 7600 years. The findings indicate paleo-fire intensity was consistent with variations in combustion types revealing by the ratio of char/soot on different timescales during the mid-late Holocene. An integrtated paleo-fire index shows that the fire activity underscores a pattern of low middle Holocene and rapidly increasing late Holocene fires, with two distinct peaks occurring during the Bronze Age and historical period. This variation aligns with the shifts observed in the char/soot ratio, indicating that enhanced flaming fires were more prevalent during the late Holocene. A comparative analysis of regional paleo-climate data has revealed that the progressive aridification of the climate, along with rising spring temperatures, contributed to the increase in paleo-fires. And the expansion of grasslands likely fueled the rise in flaming fires, thereby intensifying paleo-fire activity. Notably, we contend that human fire practices heightened the incidence of late Holoceng regional flaming fires, which in turn contributed to the intensification of paleo-fire regimes. High-intensity human activities (e.g. land reclamation, pottery production, bronze crafting) that have been prevalent since 4000 BP, along with the increased warfare since 1200 BP, were significant factors behind this outcome.